1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor integrated circuit device that uses an SOI (silicon on insulator) type semiconductor substrate, particularly, to an effective technique with which a diode type photosensor and its signal processing circuit are mounted on one chip.
2. Description of the Related Art
A conventional semiconductor integrated circuit device using an SOI substrate is shown in section in FIG. 4. In the conventional device, a diode 105 type photosensor is of so-called xe2x80x9cplanar type,xe2x80x9d and the diode 105 type photosensor and its signal processing circuit are formed in a surface semiconductor that is insulated and isolated by a semiconductor substrate 101 and a buried insulating film 102. The signal processing circuit is formed on the SOI substrate to obtain low voltage operation, low power consumption and higher operation speed, and to avoid influence of the noise.
In recent years, higher resolution has been required for line type image sensor ICs and area image sensor ICs equipped with a diode type photosensor, which in turn demands downsizing of the cell of the diode type photosensor. However, reduction of the size of the cell while keeping the S/N ratio of the photosensor at or above a given value has been difficult to attain because the noise level is not decreased in proportion to the cell size, though the absolute value of a signal per unit cell becomes small as a result of the reduction of the cell size.
The foregoing and other objects of the present invention are carried out by a semiconductor integrated circuit device comprising a semiconductor substrate having an SOI region and a bulk region, a buried insulating layer formed only in the SOI region of the semiconductor substrate, a diode-type photosensor formed in the bulk region of the semiconductor substrate and comprised of a trench and a diffusion layer disposed over side surfaces and a lower surface of the trench, and a MOS transistor formed in the SOI region of the semiconductor substrate for processing a signal from the diode-type photosensor.
In another embodiment, the diode-type photosensor further comprises an insulating film disposed in the trench. In yet another embodiment, the diode-type photosensor further comprises an insulating film disposed in the trench and a polycrystalline silicon film disposed on the insulating film for receiving an electric potential.